Influence of NiCoCrALY spraying process on oxidation resistance of 8YSZ thermal barrier coatings

The work aims to improve the high temperature oxidation resistance of thermal barrier coatings. NiCoCrAlY bond coats with different structures were prepared by detonation spraying (DS) and air plasma spraying (APS). Then, 8YSZ ceramic coatings was prepared by APS to analyze the high temperature oxidation resistance of thermal barrier coatings on bond coats with two different structures. The phase composition, microstructure and chemical composition of coatings were analyzed by X-ray diffraction, scanning electronic microscopy and energy disperse spectroscopy. The interfaces between the coatings and substrate and high temperature oxidation resistance of TBCs were investigated. DS-bond coat was dense and uniform and had less internal defects and interfacial pores with substrate, while the APS-bond coat presented more pores and low surface roughness and apparently exhibited a layered structure. A layer of Al2O3-rich oxide was formed on the surface of DS-bond coat after oxidation for 5 hours, while a layer of mix oxides (e.g. NiO, CoO, Cr2O3 and Ni(Cr,Al)2O4) was formed on the surface of APS-bond coat. Additionally, a number of micro cracks and layered oxides were found in the APS-bond coat. The weight gain of DS thermal barrier coating sample was faster than that of the APS sample in the first 5 hours oxidation and then became slowly, while the APS thermal barrier coating sample still showed high oxidation rate. Thermally grown oxide (TGO) of detonation sprayed coating still remained uniform oxide layer after 50 h oxidation. TGO layer closed to bond coat had less oxide defect. The bond coat of detonation sprayed coating has uniform and dense structure, thus preventing the oxidation during spraying and inner-oxidation during heat treatment, and promoting the formation of a dense Al2O3 layer. Finally, the diffusion between oxygen and metal atom is suppressed and the high temperature oxidation resistance of TBCs is improved dramatically. © 2019, Chongqing Wujiu Periodicals Press. All rights reserved.